Current Transients in Photondetectors · 4th student workshop, 26.03.2007 J. Stegmaier Current...

4th student workshop, 26.03.2007 Current Transients in PhotondetectorsJ. Stegmaier

Current Transients Current Transients in in PhotondetectorsPhotondetectors

Jutta Stegmaier Jutta Stegmaier ((SupervisorSupervisor: D. Lemke): D. Lemke)

44thth MPIA Student WorkshopMPIA Student Workshop

March 26March 26thth 20072007


What I‘m doing

HHERSCHEL ERSCHEL -- PACSPACS

¤¤ CharacterisationCharacterisation of Ge:Ga Detectorsof Ge:Ga Detectors

¤¤ Laboratory Simulation of Cosmic Radiation at Laboratory Simulation of Cosmic Radiation at

L2 & Curing of Ge:Ga DetectorsL2 & Curing of Ge:Ga Detectors

¤¤ Moon and Moon and beyondbeyond

3rt student workshop


What I‘m doing

HHERSCHEL ERSCHEL -- PACSPACS

¤¤ CharacterisationCharacterisation of Ge:Ga Detectorsof Ge:Ga Detectors

¤¤ Laboratory Simulation of Cosmic Radiation at Laboratory Simulation of Cosmic Radiation at

L2 & Curing of Ge:Ga DetectorsL2 & Curing of Ge:Ga Detectors

¤¤ Moon and Moon and beyondbeyond


HerschelHerschel

Mirror: 3.5 m, T ~ 80 KMirror: 3.5 m, T ~ 80 K

Launch: 2008 Launch: 2008

Orbit Orbit aroundaround L2L2

FIR FIR spacespace facilityfacility (57(57--670 670 µµm)m)

Instruments: PInstruments: PACS, SPIRE, HIFIACS, SPIRE, HIFI

HERSCHEL - In a Nutshell


HerschelHerschel






HERSCHEL - PACS

PACSPACS

PhotodetectorPhotodetector Array Camera and Array Camera and SperctrometerSperctrometer

WavelengthWavelength rangerange: 57 : 57 -- 210 210 µµmm

25x16 25x16 pixelpixel ((areaarea: 49: 49‘‘‘‘x 49x 49‘‘‘‘))


HerschelHerschel






HERSCHEL - What do we need it for?

MainGoals

¤ Galaxy formationin the earlyuniverse

¤ Star formation & ISM

¤ Galaxies

¤ Solar System

PACSPACS

PhotodetectorPhotodetector Array Camera and Array Camera and SperctrometerSperctrometer

WavelengthWavelength rangerange: 57 : 57 -- 210 210 µµmm

25x16 25x16 pixelpixel ((areaarea: 49: 49‘‘‘‘x 49x 49‘‘‘‘))


Spectrometer Camera

5x5 pixel (9.4‘‘ x 9.4‘‘ each)�� area: 49‘‘ x 49‘‘


30 60 90 120 150 180 210 240

0.0

0.2

0.4

0.6

0.8

1.0

1.2 low-stressed high-stressed

rela

tive

re

sp

on

siv

ity

wavelength [µm]

FIR Photodetectors - Design

Ge:Ga crystals: stressed by Ge:Ga crystals: stressed by

-- spring spring

-- bolt mechanismbolt mechanism

LowLow--stressed (blue):stressed (blue):

-- 200N200N

-- λλcutoffcutoff: ~130 : ~130 µµmm

HighHigh--stressed (red):stressed (red):

-- 800N800N

-- λλcutoffcutoff: ~210 : ~210 µµmm

Operation temperature: Operation temperature:

-- TTdetdet ~ 1.8K, 2.5K~ 1.8K, 2.5K

Detector

module

Ge:Ga Detector stack

PACS:

16 x 25 pixel


Detector Test Setup

•• Simulation of Simulation of inin--flightflight operationoperation conditionsconditions

•• AccurateAccurate IR IR fluxesfluxes


Characterisation

Responsivity: Responsivity: resultingresulting detectordetector currentcurrent per per incidentincident IR IR fluxflux powerpower

Infrared Telescopes on the Moon Infrared Telescopes on the Moon --

from a Robotic Precursor to a Very Large Telescopefrom a Robotic Precursor to a Very Large Telescope

To Moon and Beyond..


Today’s Infrared Astronomy

Major scientific questions:• First stars in the universe after BB• Evolution of galaxies and quasars• Cosmic Infrared Background• Star birth and formation• Extrasolar planets

Need for future: • Higher sensitivity• Very large aperture• Larger detector arrays• Ultra deep surveys

Of

http://www.ir.isas.jaxa.jp/ASTRO-F

7 billionyears

ago

present

13 billionyears

ago Big Bang

Evolution

Birth of Galaxies


Larger telescopes on moon?

SpaceAdvantages:• All wavelength accessible• Diffraction limited• Passive cooling

Limits:• High investment• No service• Apertures: 6.5 m

GroundAdvantages:• Large apertures• Upgrade of instruments

Limits:• Atmospheric windows• Thermal background &

airglow

Infrared views of the dusty universe

Opportunity Opportunity for futurefor future


Large liquid mirror telescope on the moon?Large liquid mirror telescope on the moon?

Moon

Advantages:• Large stable platform• No atmosphere• Slow rotation • Gravity• Maintenance, upgrade

But:• Manned flights stopped 30 years

ago

Large liquid mirror telescope on the moon

Advantages:• Gravity shapes perfect surface• Large aperture for low costs• Light weight structure

Limits:• Zenith telescope

→ Ideal for deep observations


Status of liquid mirror telescopes

On ground (Borra et al.): • Proven for 6m• Liquid: Mercury• Performance: Seeing limited

Challenges:• Surface ripples• Smooth & precise rotation

Large Zenith TelescopeMaple Ridge, BC

D=6m, f/1.5, CCD: 2Kx2K


Large IR lunar telescope

Basic concept• Diameter > 20 m• 1 < λ < 20µm (liquid mirror telescope)• 20 < λ < 350µm (interferometer of solid mirrors)• T < 100K• Deployed & operated robotically

Technological challanges• Liquid • Central bearing

Expected performance• 3 x spatial resolution of JWST• ~10 x higher sensitivity• F~100pJy

Operation• Zenith pointing → no steering, easy mounting• Polar location preferred → long exposures without tracking

R. Angel, T. Connor (2004)


Lunar orbit

.

0.2° camera FOV

2 sqd in 18 yrs (1000x HDF)

Sky coverage

1.55°


Pole selection for large lunar telescope

Shackleton crater (89.9°S)

• Permanent shadow

• Max. illumination 80-90%

• Large Magellanic Cloud

South Ecliptic Pole 15 x 15 arcmin

Winter (Clementine)

Peary crater (88.6°N)

• Permanent shadow

• Eternal light at rim

North Ecliptic Pole 15 x 15 arcmin

Bussey et al., 2005

Summer (Clementine)


Is there need for a precursor mission ?

HowHow darkdark isis thethe skysky??

IsIs therethere dustdust??

TechnologicalTechnological

challengeschallenges??


Nearly no atmosphere (~3 x 10-15 bar) & no dipole magnetic field (~10-9 T)

• Faint atmospheric emission?

• 100 K < T < 400 K

• High ionizing radiation background

• Impacts: meteorites & micrometeorites

Dust• Origin: meteorites • Levitation near terminator (10-30cm)• Thin dust atmosphere (>100km) ?

Lunar environment

Lunar rays sketched byApollo 17 captain Cernan (NASA)

Need for precursor mission• Study cleanliness of lunar environment• Additional scientific benefits


1.) Absolute surface brightness of zodiacal light

2.) Measurements of EBL (constraints on cosmology)

Scientific benefit


Precursor design

First small instrument• Piggyback on lunar lander• Wavelength: 0.4 – 2.5µm• FP or interference filter: λ/∆λ~1000• Prism• Spatial resolution ≤ 1 arcmin, FoV ~ 5°• Elevation scans: 0-90°

Logistics• Location of landing: back side, mid-latitude,

pole,..• Operation time: ≥ 14 days• Cooling: passive cooling in crater or by

radiation shields, new moon

Next• Liquid mirror precursor: n=1.5m LMT

Solar Fraunhofer lines

Optical scheme


Conclusion

Will the moon be a German?

„Wird der Mond ein Deutscher?“(BILD)


Thanks for your interest !

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